Domestic water treatment devices are known in the art. Among these devices are self-contained systems which process water in batches. Examples of batch devices are pitchers/carafes and larger reservoirs where treated water is poured, for example, from a spigot. These self-contained systems typically have upper and lower chambers separated by a filter cartridge. They rely on gravity to force water from the upper chamber, through the cartridge, and into the lower chamber, thereby producing treated water.
The presence of unwanted and potentially harmful contaminants in water, especially drinking water, is of concern to many people. This concern creates a desire for water treatment devices in the home and elsewhere. Many water treatment devices and methods have been developed to remove or neutralize chemical and particulate contaminants. Some of these devices and methods incorporate chemically active materials to treat the water. For example, activated carbon is capable of removing the bad taste and odor from water as well as chlorine and other reactive chemicals. Ion exchange resins are useful for removing metal and other ions from water. However, no single material or chemical has been found that will remove all contaminants.
In addition to chemical and particulate contaminants, water often contains biological contaminants. These contaminants often can not be entirely removed by activated carbon, ion exchange resins, or other chemically active water purifiers. The biological contaminants may be susceptible to harsher chemical treatment, but such chemicals are, typically, themselves contaminants or can not be easily incorporated in gravity-fed treatment devices, especially those for household use. In addition to being resistant to removal by standard chemical means, many of these biological contaminants, such as protozoan cysts like cryptosporidium, are only a few microns in size.
Because of their small size and the relative unavailability of suitable chemical removal methods for these biological contaminants, a gravity-fed water treatment device which can remove protozoan cysts and still retain satisfactory flow rate has been very difficult to develop. Present devices which filter cysts out of water require pressurization, either from the tap or by manual pumping, to achieve a satisfactory flow rate. However, such devices are relatively complex and expensive, and in the case of manual pressurization systems, harder to operate. Thus, there is a need for a gravity-fed water treatment device that is capable of removing biological contaminants, including cysts like cryptosporidium, while providing an acceptable flow rate.